The invention concerns a procedure to separate mixtures containing organic components, by means of high pressure extraction.
It is known that numerous gases have a high solvent capacity, even for heavy substances, if they are used as solvents under high pressures. Preferably, the gases are used under super critical conditions in respect to pressure and temperature. It is a specific advantage of high pressure extraction that the characteristics of the solvent used, e.g., solvent capability and selectivity, can be varied by simple changes of pressure and temperature. Many procedures have been developed which utilize these characteristics, e.g., as known from DE-AS No. 14 93 190, DE-PS No. 20 05 293, DE-OS No. 21 06 133, DE-OS No. 21 27 596, DE-PS No. 21 27 642, DE-OS No. 22 12 281 and DE-OS No. 26 37 197.
From DE-OS No. 27 37 793, it is further known how to use a multi-component gas as a solvent. Hereby a so-called carrier is added to the actual gas serving as a solvent, whereby the solubility of specific substances is significantly increased.
In principle, the installations for implementing the high pressure extraction procedure consist of an extractor and a separator. In the extractor, the solvent flows through the mixture and thereby dissolves certain substances contained in it. These are segregated from the solvent as far as possible in the connected separator. Since the quantity of contained substances transported into the separator per unit solvent is generally small, large quantities of solvent must flow through the extractor in order to achieve satisfactory levels of extraction. For economical reasons, it is therefore necessary to return the solvent from the separator into the extractor for re-use, after it has been freed from the contained substances to the greatest extent possible, and to maintain this circulation until the desired level of extraction has been reached.
There are numerous variations of the basic principle of this procedure. One may mention, e.g., fractionated extraction or extract recovery. Hereby, several extractors and separators are used under varying pressure and temperature conditions, and/or the procedure is carried out in sequential steps under these conditions. However, the described basic principle applies for all of these levels of the procedure.
The segregation of the dissolved contained substances from the solvent is of utmost importance for the economy of the high pressure extraction procedure. Unsatisfactory segregation has a negative influence on the economy of the procedure and limits the charge capacity of the solvent for continued extraction. The segregation in the separator is carried out either by means of pressure and temperature changes, or by using different separator fillers, which function, e.g., according to the principles of adsorption, gas scrubbing, or ion exchange.
Some of these segregation procedures have significant disadvantages. In order to achieve far-reaching segregation of the dissolved substances by means of pressure and temperature changes, there will mostly have to exist great pressure and temperature differences between the extractor and the separator. On one hand, this means that the process becomes significantly more expensive, and on the other hand, there is often such a strong thermal load on the extract that the quality and usefulness thereof is limited. In principle, isobaric or isothermic segregation by means of adsorbents, ion exchangers, or scrubbing solutions is thus more advantageous. In this procedure, the main disadvantage is that the extract must be repeatedly recaptured from the separator stage in subsequent steps of the process. This is technically costly and uneconomical; occasionally it is even impossible. Thus, for instance, in large scale application of high pressure extraction for decaffeinating raw coffee, the extracted caffeine is adsorbed on active carbon without being recovered and utilized further.